A vice perfectly designed for holding a PCB whilst working on it.  Unclamp the free end, position your PCB between the jaws and clamp it down.  The spring loaded jaw then holds the PCB tight whilst allowing easy removal and reinsertion whenever you need to check on your soldering.

You'll need 3x30mm M3 countersunk bolts, 2x10mm M3 countersunk bolt (or some superglue) and two “pen” springs; stolen from clicks pens in your junk draw.

See the combines stl/3mf file for ideal orientation; basically print everything upside down so the smooth bottom surface run against each other.

The small handle on the sprung jaw is optional; but makes one handed removal and insertion easier.  I recommend glueing some silicon to the bottom to prevent it from sliding around as you work.